1. Field of the Invention
The disclosure generally relates to a communication system, and more particularly, relates to a communication system for reducing SAR (Specific Absorption Rate).
2. Description of the Related Art
With the progress of mobile communication technology, portable electronic devices, for example, portable computers, mobile phones, multimedia players, and other hybrid functional portable electronic devices, have become more common. To satisfy the demand of users, portable electronic devices usually can perform wireless communication functions. Some functions cover a large wireless communication area, for example, mobile phones using 2G, 3G, and LTE (Long Term Evolution) systems and using frequency bands of 700 MHz, 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, 2100 MHz, 2300 MHz, and 2500 MHz. Some functions cover a small wireless communication area, for example, mobile phones using Wi-Fi, Bluetooth, and WiMAX (Worldwide Interoperability for Microwave Access) systems and using frequency bands of 3.5 GHz, 5.2 GHz, and 5.8 GHz.
However, current portable electronic devices can not prevent users from being exposed to electromagnetic waves. For example, when a wireless communication operation is performed, a mobile phone transmits electromagnetic waves which are near to a head of a user, for a mobile phone. Therefore, governments have formulated criterion as to how much electromagnetic waves is safe for a human body to absorb, such as specific absorption rate, or the so-called SAR criterion. SAR is a measure of the rate at which energy is absorbed by the human body when exposed to a RF (Radio Frequency) electromagnetic field. It is defined as the power absorbed per mass of tissue and has units of watts per kilogram (W/kg). In Taiwan, the criterion of SAR in electronic devices is similar to Europe, below 2 W/kg.